In many disciplines, a pressurized fluid must be supplied in precise quantities. Usually, the quantity of fluid supplied is controlled by regulating the flow of the fluid. Fluid flow is independent of conduit size, supply pressure, and the like, and controlling the flow rate ensures that a precise quantity of the fluid is delivered where required.
The present invention is of particular significance when used to control the flow of gasses at relatively low flow rates and will be described in detail below in that context. But the present invention may have application to other fluids such as liquids and to relatively large flow rates. The scope of the present invention should thus be determined with reference to the claims appended hereto and not the following detailed description.
One example where the quantity of a gas supplied must be precisely controlled is the delivery of a gas to a medical patient. In this context, a gas is mixed with air supplied to the patient through a ventilator to obtain a desired effect. If too little gas is supplied to the patient, the desired effect may not be obtained. On the other hand, too much gas may be toxic to the patient. Other examples where precise quantities of gas must be supplied include scientific and medical testing, industrial processing, and scuba diving.
A primary impediment to maintaining a constant flow of gas is that the pressure at which the gas is supplied may be unknown or variable. Often, the source of the pressurized gas is a pressurized tank or compressor. The pressure of the fluid supplied by either of these sources can fluctuate significantly. For example, as the quantity of gas within a pressurized tank decreases, the pressure of the fluid flowing from the tank will decrease. Accordingly, in many systems in which the flow of a gas is important, the flow rate must be measured and monitored and the system adjusted as necessary to maintain the flow rate within predetermined limits.